A preliminary objective of this study is to demonstrate stereoscopic discrimination in a normal adult cat. This will be done by training cats to an operant discrimination between two projected stereoscopic patterns. Concurrently, similar training will be given to normal binocular kittens, and age-mates deprived from birth of input to one eye. Performance of these animals will be compared to determine whether, and to what extent stereopsis is impaired by monocular deprivation. A second objective is to determine the trainability of stereoscopic discrimination in deprived animals, should significant impairment be observed. These findings comprise essential data for evaluating current neurophysiological models of binocular vision, since such models are based upon electrophysiological studies of cortical response in normal and restrictively-reared cats with behavioral data essentially lacking. In addition deprived and normal eyes will be compared in terms of shapes of refracting surfaces (cornea and lens), axial length, intraocular pressure, and refractive status. Such measurements represent a new body of data on the effects of monocular deprivation. Later studies will test stereoscopic discrimination in animals that have been deprived of binocular exposure, but without deprivation of light or pattern for either eye. Results will be closely compared to those in earlier studies. Correlative neurophysiological data may become available in later stages of the project.